Does your 4.0 stroker run like crap when cold? - JeepForum.com
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Unread 06-11-2013, 04:59 PM   #1
95yj0645
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Does your 4.0 stroker run like crap when cold?

Hey all I built a 4.6L stroker and it runs real crappy at idle like WAY too "lopey". Once it hits operating temps it runs awesome just has a slight cam lope. Even when it is cold it still runs good when you get in the gas its just at idle. I am running 24lb injectors and honestly they might be too much for it because I have a map sensor adjuster built and didnt even need to use it on this stroker so it obviously has plenty of fuel. My cam is a comp extreme 4x4 cam I believe its a stage 1 nothing too ridiculous. How does everyone elses run at idle when cold? This engine has RIDICULOUS power for a jeep. I couldnt be happier with how it turned out, but I just wish it didnt run like it does when I cold start it. suggestions?

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Unread 06-11-2013, 05:36 PM   #2
superj
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Mine has a Holley four barrel on it but runs great. All stock parts though, no custom cam or anything
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Unread 06-11-2013, 05:39 PM   #3
jsawduste
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I run a stroker with plenty of cam.

Cold is open loop running off the ECM programming till the O2 sensor warms up and coolant temp rises. Returns to open loop at throttle opens above 75-80% and relies heavily on the MAP sensor output voltage for injector duty cycle.

Describe a cold start. How long till the symptoms go away ? 30 seconds, 60 seconds or ??

Here are some thoughts and checks.
Fuel pressure too high
O2 sensor heater malfunction
Not enough airflow at idle
Poor vacuum signal to the MAP
Coolant temp sensor malfunction (not to the gauge but to the ECM)
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Unread 06-11-2013, 05:41 PM   #4
jsawduste
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Quote:
Originally Posted by superj View Post
Mine has a Holley four barrel on it but runs great. All stock parts though, no custom cam or anything
To entirely different induction systems and intake/exhaust events, no relevance.

Have you yet to take the engine down to verify that it even is a stroker ?
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Unread 06-11-2013, 05:47 PM   #5
95yj0645
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Yeah mine is EFI. It only takes about 5 minutes of driving for it to start smoothing out.
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Unread 06-11-2013, 05:48 PM   #6
95yj0645
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I built the engine myself lol I can verify that it is a stroker...
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Unread 06-11-2013, 06:16 PM   #7
jsawduste
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Simple things first.
What is you fuel pressure at idle and amount of vacuum at the MAP during cold start.
What size TB are you running ?
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Unread 06-11-2013, 06:38 PM   #8
superj
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Just a local guy checked it and said it had the signs. He had built one before so he said he would look.

I have not opened anything on it to check anything, myself. All I know is it has a lot more pick up and power then my friends freshly overhauled 4.2 in his 86 cj7. I kill him light to light and he is in a stick
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Unread 06-11-2013, 09:43 PM   #9
95yj0645
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My fuel pressure is 38-39 psi iirc it's been about a month since I last had a guage on it. Not sure about map vacuum .. I will bring my vac guage and a tee fitting home from work and check it this weekend
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Unread 06-11-2013, 10:07 PM   #10
jsawduste
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Once warm, any stumble as the engine returns to idle from speed ?

Any surging at low RPM (less then 1000) light throttle ?

No mention of an A/F gauge so I am guessing you are not running one.

Here is where I am going with this. I found that my idle and coast down to idle caused an excessively rich A/F ratio. Sometimes a stumble and in rare occasions a stall. My A/F ratios were a bit high and the IAC could not react fast enough. Started drilling a small hole in the throttle plate to allow for more air. .1094 drill bit is where I am at now. BIG change in idle and coast down. No more surging and drive-ability is far improved.

Second I got rid of that electric fan. I do not like electric fans, period. The Spal had the engine temp cycling from 185 to 210 and back down. The ECU was constantly adjusting for coolant temp.

The factory shroud, fan and fan clutch keeps the engine at 180 to 190. A 10 degree change vs the 25 of before. Result is better performance, mileage and drive-ability because the ECU is able to do a better job of calibration due to temperature stability. In fact, given a choice I`d like to see it run a bit warmer say 195 to 205. Yes I am running a 195 stat but with a 3/16ths bleed hole.
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Unread 06-11-2013, 10:24 PM   #11
95yj0645
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That sounds exactly like what mine is doing . I really like your "drill throttle plate" idea because I have a spare TB. As far as stumble coming off of higher speeds I haven't noticed because my exhaust is so leaky at the muffler. Running a full exhaust system this weekend also. Def has a slight stumble when first taking off but like you said as soon as it's in the gas the jeep comes to life and runs like a scalded dog. My fuel mileage I feel could be better because I'm not really a lead foot or drive faster than 55. It's only getting around 15 mpg. I feel like 18-19 is very achievable with my gearing and tire size.
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Unread 06-12-2013, 05:44 AM   #12
jsawduste
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If you do the TB plate hole start SMALL and work your way up. Give the ECU time to adjust to the new air flow changes. I worked my way up to a 1094 in 4 or 5 steps. You may find that a different size hole works better for you.

The plate is aluminum so if a small piece of residue from drilling gets away from you then no worries. It will pass through the engine with no harm.
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Unread 06-12-2013, 05:47 AM   #13
95yj0645
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I will Definately try that. Where exactly did you drill at on the throttle plate ? Towards the edge?
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Unread 06-12-2013, 06:15 AM   #14
jsawduste
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Just off the shaft centered in the plate.
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Unread 06-12-2013, 10:04 AM   #15
95yj0645
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I will post my results tonight if I can find a small enough bit here at the shop.
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